Sidney Crosby has the vaccine-preventable disease, the Pittsburgh Penguins announced the diagnosis in a news release Sunday morning.
According to the release, Crosby will be "monitored daily, but specialists believe he should be through the infectious period by Monday."
Crosby was held out of the Penguins' past two games for "precautionary reasons" as the team awaited additional test results -- his initial test results came back negative, a source told ESPN.com -- and he will also miss the team's game against the Tampa Bay Lightningon Monday night.
Crosby received a booster shot against the virus before traveling to Russia for the Winter Olympics in February, and initial tests done a couple of weeks ago indicated that Crosby was not in any danger.
"It came as a bit of a surprise," team doctor Dharmesh Vyas said. "Every indication was that he was well protected against the disease."
The reigning Hart Trophy winner joins the ranks of 11 other players who have contracted the disease. Players from the Anaheim Ducks, Minnesota Wild, New Jersey Devils and New York Rangers have all been affected.
The Rangers confirmed Sunday that center Derick Brassard has the mumps. He is the second member of the team to be affected by the disease this season.
The Penguins have aggressively tried to prevent the disease from spreading, having players and staff undergo testing earlier in the month. Vyas said Crosby had no major symptoms, pointing out that the swelling that usually accompanies mumps is present on both sides of the face. Crosby had swelling on only the right side of his face -- swelling the team believed was related to a salivary gland injury sustained in a game against Carolina on Nov. 29.
"He did not have a classic presentation of mumps," Vyas said.
The setback for the team's second-leading scorer is the latest unusual medical development for the Metropolitan Division-leading Penguins. Forward Pascal Dupuis is out for the regular season because of blood clots. Defenseman Olli Maatta missed two weeks in November after a cancerous tumor was removed from his thyroid. Maatta is currently dealing with an unspecified injury the team said is not related to the thyroid surgery or the mumps.
"In our case we're going through a period here that's pretty rough," general manager Jim Rutherford said. "It's a period that builds character, and if you can get through it, it's going to help you in the long run."
In light of the mumps situation, the league sent out a memo in conjunction with the NHL's Infection Control Subcommittee last month, providing clubs' medical personnel and trainers with recommended guidelines and protocols to assist in both the treatment and prevention of the disease.
Dr. Greg Wallace, a lead epidemiologist at the Center for Disease Control and Prevention in Atlanta, told ESPN.com that, considering the lengthy incubation period of the mumps, it's virtually impossible to predict how long this outbreak will affect the league.
The CDC receives anywhere from a couple of hundred to a couple of thousand reported cases of the mumps annually.
The Associated Press contributed to this report.
Sidney Crosby Diagnosed With Mumps
ESPN NHL writer Katie Strang reports the latest on Sidney Crosby, who has been diagnosed with the mumps.